Deep drawing method

ABSTRACT

Method for deep drawing metallic articles from sheet material utilizing a die plate having a female cavity, a holddown member for holding sheet material against the die plate around the cavity, and a male die punch for drawing the sheet material into the female cavity. Prior to placing the sheet material over the female cavity, the cavity is substantially filled with a liquid lubricant. The hold-down acts to hold the sheet material against the die plate so as to prevent wrinkling during drawing in a conventional manner, and the male die draws the sheet material into the liquid filled cavity forcing the liquid lubricant between the under surface of the sheet material and the die plate.

United States Patent 91 Granzow *Nov. 6, 1973 [54] DEEP DRAWING METHOD 3,516,274 6/l970 Graham et al. 72 57 [75] Inventor: Wayne G. Granzow, Middletown, FOREIGN PATENTS OR APPLICATIONS Ohm 666,565 9/1938 Germany 72/43 [73] Assignee: Armco Steel Corporation,

Middletown, Ohio Primary Examiner-Charles W. Lanham Assistant Examiner-45. M. Combs 1 Notice: The portion of the term of this patent Subsequent to Nov. 1990, Attorney John W. Melville et al. has been disclaimed. [57] ABSTRACT 22 Fil (1: un 14 1972 1 c J e Method for deep drawing metallic articles from sheet PP'- 262,676 material utilizing a die plate having a female cavity, a holddown member for holding sheet material against 52 u.s. Cl 72/41 72/57 72/60 the Plate around the cavity, and a male Punch I for drawing the sheet material into the female cavity. 51 1 Int. Cl B21d 22/22 Placing the Sheet material the female [58] Field of Search I: 72/39 41 43 44 the cavity is suhstahha'ly filled with a quid 2 60 350 lubricant. The hold-down acts to hold the sheet material against the die plate so as to prevent wrinkling dur- [56] References Cited ing drawing in a conventional manner, and the male die draws the sheet material into the liquid filled cavity UNITED STATES PATENTS v forcing the liquid lubricant between the under surface 2 mfig g of the sheet material and the die plate. l or 2,649,067 8/1953 Kranenberg 72/6! 5 Claims, 3 Drawing Figures DEEP DRAWING METHOD BACKGROUND OF THE INVENTION This invention relates to the deep drawing of metallic articles from sheet material. As ordinarily understood in the art, and as used in this specification, the phrase deep draw refers to a drawing operation wherein the depth of draw is greater than the'radius of the part being formed.

The production of manufactured articles by a .drawing operation from sheet material is old and well known in the art. The equipment for .a conventional deep drawing operation includes a press having a die plate, a hold-down ring, and a punch. The die plate includes a female cavity configured toform the external surface of the part desired. The hold-down ring or member is provided to press the sheet material against the die plate. As is well known in the :art, the hold-down ring restricts the material in the flange so that it does not wrinkle excessively as it is drawn into the female die.

The final component, the male punch or ram is reciprocated by the press.

In operation according to conventional practice, the surface of the die plate and female cavity may be coated with a suitable lubricant. The sheet material to be drawn is generally also coated with a lubricant. The sheet of material is placed over the female cavity, and the hold-down put into position toho'ldlthe sheet material against thedie plate. It will of course be understood that in ordinary practice, the hold-down member will correspond in configuration to the shape of the female cavity. The male punch is reciprocated todraw :the sheet material into the female cavity, thereby forming the finished part.

Still according to conventional practice, there are three primary factors affecting a drawing operation. The first is the hold-down pressure. As previously indicated, the hold-down serves to keep the material from wrinkling as it isdrawn into the female cavity. Generally considered, the thinner the material, the proportionately greater hold-.down pressure required. Of course, a decrease in hold-down pressure will permit somewhat deeper drawing, but generally at the-expense of wrinkle formation.

The second important factor is lubrication. As just indicated, ample quantities of lubricant generally must be supplied to the sheet material and the die plate. The type of lubricant and method of application, as known in the art, will significantly affect the drawing operation.

The third main factor in drawability is size of the blank. On the one hand, it will be apparent that the blank must be large enough to produce the part desired. At the same time, it is well recognized that the smaller the blank, the easier it is to draw.

The importance of blank size is sometimes expressed in terms of the draw ratio." In the case of a cylindrical part, this is equal to the diameter of the starting blank over the diameter of the cup being drawn. Literature in the art at this time indicates that the maximum draw ratio range is from 1.611 to 2.3:].

All of the foregoing is well known and established in the art. Exhaustive data are available describing appropriate lubricants, hold-down pressures for various draw ratios, etc. None of this information, per se, .forms a part of this invention.

The art has also developed at least two hydrome- .chanical drawing or forming operations. One of them,

known as hydro-mes contemplates that the part to be produced is formed by forcing a sheet of material by means of a pressure-regulated hydraulic cushion againsta down-stroking drawing punch. In other words,

the sheet of material to be formed :is placed over an hydraulic chamber. As the drawing punch descends, the pressure in the hydraulic chamber is regulated by a suitable valve mechanism so that the controlled hydraulic cushion is effective to form. the material against the punch, thus taking on its exact shape.

A somewhat similar process is known in the art as hydroform. This process contemplates a double acting hydraulic press with an upper forming chamber and a lower hydraulic ram to actuate the punch. The controlled fluid pressure forming chamber contains hydraulic fluid which is isolated from the part being formedby means of a flexible diaphragm. The preseure within the chamber is programmedin relation to the specificpart being formed. As the punch is moved upwardly, the pressure in regulated to form the part around the punch.

The instant invention is directed to a method for deep drawing of metallic articles from sheet material.

More specifically, it is an object'of this invention to I providea method for deep drawing which can achieve a drawing ratio in excess of 2.5:].

It is a further object of this invention toprovide a method which will permit deep drawing of articlesfrorn sheet material utilizing ordinary grades of drawing steel as opposed to the more expensive extra deep drawing SUMMARY OF THE INVENTION Broadly considered, the method of this invention relates to the deep drawing of metallic articles from sheet material utilizing conventional press equipment. The invention contemplates the provision of a die plate having a female cavity. This cavity is first substantially fully filled with a liquid'lubricant. The sheet'material is then placed over the cavity and held against the die plate so as to prevent wrinkling during drawing by a suitable hold-down mechanism. A male punch then draws the sheet material into the cavity forcing the liquid out of the cavity between the underside of the sheet material and the die plate, thereby producing a finished part.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematicillustration showing the components in the starting position.

FIG. 2 is a schematic illustration similar to FIG. 1 showingthe components shortly after the beginning of the drawing.

FIG. 3 is a schematic illustration showingthe components at the completion of the draw.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, the components utilized in the practice of this invention have been schematically illustrated in the starting position. These components include a die plate indicated generally at 10. It will of course be understood that the die plate 10.will be supported on the base of a suitable press which is not shown. The die plate will be provided with a female cavity 12 which may be configured to the external shape of the finished article desired. It has been found possible to form some shapes using only the hydraulic pressure generated in the die cavity. In these instances, only that portion of the female cavity containing the draw radius need conform to the shape of the part being formed, with the remaining portion serving as a reservoir for the liquid lubricant. In the embodiment illustrated, the cavity 12 is configured to form a simple cup.

In any case, the configuration of the die cavity 12 and the punch 18 may conform in all respects to conventional practice. That is, the draw radius 14 at the top of the cavity and any radius such as 16 at the bottom of the punch conform to conventional practice. Ordinarily, the radius 14 should be as great as possible to facilitate drawing, but cannot be too great because of the possibility of wrinkling due to unsupported metal being drawn into the cavity. Typically, the draw radius 14 will approach but not exceed ten times the thickness of metal being drawn.

The male punch is indicated at 18. This punch will of course be vertically reciprocated by a suitable press mechanism which is again not illustrated in the drawings. The clearance between the female cavity 12 and the male punch 18 should be determined in accordance with well known conventional practice.

The radius 16 at the bottom of the punch 18 will vary with the forming limits of the material utilized in accordance with conventional practice.

The material hold-down is indicated schematically at 20. The hold-down is configured to completely surround the female cavity 12, and is urged downwardly against the die plate 10 by a suitable mechanism, not illustrated. In accordance with conventional practice, the inside edge of the hold-down should be disposed at least at the outside edge of the draw radius 14, and may extend inwardly toward the punch. As is known in the art, the hold-down mechanism prevents wrinkling of the sheet material as it is drawn into the cavity 12. In accordance with conventional practice, the pressure exerted by the hold-down will vary with the thickness of material and depth of the article being drawn. As previously indicated, the interior edge of the holddown should be at the edge of the radius 14 so as to minimize the extent of unsupported metal being drawn into the female cavity 12.

A suitable sheet of material being drawn is indicated at 22. For clarity of illustration, it will be observed that in the three Figures, the sheet 22 is spaced slightly above the top surface of the die plate 10 and in contact with the bottom surface of the hold-down 20. It will of course be understood that in the starting position, the sheet of material 22 rests upon the top surface of the die plate 10, and is firmly held in that position by the hold-down 20.

All of the components thus far described are conventional and well known in the art.

The essence of this invention resides in the surprising discovery that when utilizing this conventional equipment, significantly larger draw ratios can be achieved by substantially filling the cavity 12 with a liquid lubricant. The liquid lubricant is indicated in the Figures at 24. It will be observed that the cavity 12 has been filled with liquid lubricant to a level approaching its top surface.

The method of this invention contemplates the substantial filling of the cavity 12 with liquid lubricant prior to the placing of a sheet of material 22 in position over the cavity 12. The entire top and bottom surface of the sheet material 22 may be provided with a suitable lubricant in accordance with conventional practice. The hold-down 20 is actuated to firmly hold the sheet material 22 against the top surface of the die plate 10, and the drawing operation will proceed as indicated schematically in FIGS. 2 and 3. The liquid lubricant 24 is of course substantially incompressible and confined by the cavity 12. Therefore, as the punch 18 draws the sheet material 22 into the liquid lubricant filled cavity 12, the liquid must go someplace. Actual tests have established that the liquid lubricant is forced between the side walls of the cavity 12 and the sheet material, and then outwardly between the top. surface of the die plate 10 and the bottom surface of the sheet material 22 as indicated by the arrows 25. This movement of liquid lubricant along the path described continues during the entiredrawing operation. There is a balance between the force of the punch and the liquid lubricant coming out of the cavity creating a hydraulic cushion between the sheet material and the die plate.

The actual experimentation referred to above has successfully drawn a cup having a diameter of four inches from a ten inch square sheet of material. In other words, a drawing ratio of 2.5:1 has been successfully achieved with ordinary low carbon drawing quality sheet steel. With conventional drawing practice and using the same dies, the limiting drawing ratio was found to be 1.88:1 for the same material.

The precise theory of operation of this invention is not fully understood. While not wishing to be bound by theory, applicant believes that the invention results in a continuous, forced lubrication between the top surface of the die plate and the under surface of the material being drawn. In addition, it will be observed in FIGS. 2 and 3 that the sheet material is not being formed by the radius 14 at the top of the die cavity. Rather, the metal is forced slightly upwardly by the pressure of liquid lubricant in the cavity 10 as the punch 18 moves downwardly. It is believed that this action provides a liquid draw radius, and eliminates the metal to metal contact occasioned in prior practice.

In keeping with the foregoing theory, the phrase liquid lubricant is used in this specification in terms of its effect rather than composition. In other words, in the case of a polished die and punch, water will provide a suitable forced lubrication. In the case ofnew tooling and for more severe ratios, it is desirable to add a small quantity of any water soluble lubricant to the water.

It should also be apparent that the liquid, whatever its composition, cannot act as a lubricant until it is forced out of the die cavity. Therefore, the lower the level of liquid in the cavity, the more the sheet must be deformed before the forced lubrication takes effect. In the experimentation referred to earlier, 2.5:1 draw ratios had been obtained with the liquid one-half inch below the top surface of the female cavity. When the liquid was one inch below the surface, the material failed before touching the liquid. Thus, it is desirable in practice that the cavity be substantially filled with liq uid lubricant in order to insure that the forced lubrication takes place as early in the draw as possible.

It is fully within the scope of this invention to provide a suitable arrangement for containing the liquid forced out of the die cavity, and returning it to the cavity as the punch and part are withdrawn. By way of example, a sheet metal dike can easily be provided surrounding the hold-down. When the punch and part are withdrawn from the die cavity, substantially all of the liquid will be returned to the cavity.

It is believed that the foregoing constitutes a full and complete disclosure of this invention, and no limitations are intended except insofar as set forth in the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method of deep drawing metallic articles from sheet material including the steps of providing a die having a top surface and a female cavity terminating at said top surface in a die radius, placing a sheet of material over said cavity, holding said sheet of material against said die top surface whereby to restrict wrinkling of said sheet during drawing, and drawing said sheet of material into said cavity with a male die punch: the improvement comprising the steps of substantially filling said cavity with a liquid lubricant prior to drawing and continuously forcing liquid lubricant out of said cavity during drawing, all liquid lubricant forced out of said cavity being forced between said material being drawn and said die radius and die top surface in a direction opposite to the flow of said material being drawn.

2. The method claimed in claim 1 wherein said liquid lubricant is forced out of said cavity by the entrance therein of said punch and said material being drawn.

3. The method claimed in claim 1 wherein said liquid lubricant is water.

4. The method claimed in claim 2 wherein said liquid lubricant is water.

5. The method claimed in claim 4 wherein said water contains a small quantity of water soluble lubricant.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 7 9, Dated November 1973 l fl WAYNE G. GRANZOW It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

At the top of the first page of the patent the sentence "The portion of the term of this patent subsequent to November 6, 1990, has been disclaimed." should be deleted and I the following sentence substituted therefor --'Ihe entire term of this patent is dedicated to the Public of the United States.

Signed and sealed this L th day of June 19714,.

(SEAL) Attest: v V

c. MAESEA ED NN I EDWARD M.ELET0HER,JE. E

Commissioner of Patents Attesting Officer R PC1-1050 (10459) USCOMM-DC ooa'Io-Pea I I I i ".5, GOVERNMENT PRUTING OFFICE: "I. O-lI-SJ 

1. In a method of deep drawing metallic articles from sheet material including the steps of providing a die having a top surface and a female cavity terminating at said top surface in a die radius, placing a sheet of material over said cavity, holding said sheet of material agAinst said die top surface whereby to restrict wrinkling of said sheet during drawing, and drawing said sheet of material into said cavity with a male die punch: the improvement comprising the steps of substantially filling said cavity with a liquid lubricant prior to drawing and continuously forcing liquid lubricant out of said cavity during drawing, all liquid lubricant forced out of said cavity being forced between said material being drawn and said die radius and die top surface in a direction opposite to the flow of said material being drawn.
 2. The method claimed in claim 1 wherein said liquid lubricant is forced out of said cavity by the entrance therein of said punch and said material being drawn.
 3. The method claimed in claim 1 wherein said liquid lubricant is water.
 4. The method claimed in claim 2 wherein said liquid lubricant is water.
 5. The method claimed in claim 4 wherein said water contains a small quantity of water soluble lubricant. 